1. Field of the Invention
The present invention relates generally to blades and vanes for gas turbine engines and particularly relates to the cooling of such airfoils using a formed insert with perforations. The insert also functions as a bonding foil at the joints formed between bonded surfaces of the airfoils.
2. Description of Prior Developments
Traditionally, airfoils for gas turbine engines have been internally cooled using various inserts and baffles which are inserted into the airfoils during the manufacturing cycle to direct cooling fluid against the internal surfaces of the airfoils in the form of numerous high velocity air streams or air jets. Such cooling, known as impingement cooling, is usually quite effective in maintaining the temperature of the airfoils within acceptable limits.
Unfortunately, the design of such internally cooled airfoils is compromised by the need to position the inserts or baffles within the interior of the airfoils after they have been formed. That is, the interiors of the airfoils must be dimensioned to allow the subsequent assembly of the baffles therein. This can limit the shape of the final airfoil contours.
It is also known that by allowing the cooling air to flow over the outer surface of an airfoil in the form of a thin film, the airfoil will run cooler. Generally, however, the more cooling air which is used to cool the airfoils, the less efficient is the operation of the gas turbine engine.
Accordingly, a need exists for an airfoil which is internally-cooled with inserted baffles and which is fabricated in such a manner that the airfoil design is not compromised by the necessity of providing internal clearances for positioning and assembling the baffles therein.
Moreover, a need continually exists for more efficient use of valuable cooling air in order to improve the overall efficiency of gas turbine engine performance. One approach to improving the effectiveness of the cooling air is to improve the rate of heat transfer from the heated airfoil surfaces being cooled to the cooling fluid flowing over these surfaces. By combining several modes of heat transfer in a single cooling air circuit, a more efficient and effective level of heat transfer may be achieved.